A valve device and a valve disk of the type initially mentioned are known from the document EP-A-0 834 689.
Valve devices of this type are used, for example, in the foodstuff industry for the production of products, such as UHT milk, yoghurt and the like.
In valve devices of this type, there are stringent requirements as regards the reliable separation of the media carried by the at least two pipelines. The valve arrangement for the selective closing and release of the connecting orifice, via which the two pipelines can communicate with one another, must therefore, in the closing position, ensure that the connecting orifice is reliably sealed off. Moreover, the valve arrangement, including the at least one valve seat, must be capable of being cleaned thoroughly and, in particular, be sterilizable.
In order to satisfy these requirements, valve devices of the type initially mentioned are designed as double seat valves.
In the known valve device, the valve arrangement has, at the connecting orifice between the connection pieces of the at least two pipelines, two valve seats for two valve disks, an upper valve disk and a lower valve disk. To release the connecting orifice, the upper valve disk and the lower valve disk are moved downward, that is to say the known valve device is a downwardly opening double seat valve.
Between the two valve disks is located a leakage space which possesses an outflow via a tubular extension on the lower valve disk. In the closing position of the valve arrangement, in which the connecting orifice must be sealingly closed, a leakage and, consequently, a malfunction of the valve arrangement in its closing position can be detected via an outflow of a medium from the tubular extension.
The two valve disks are movable not only jointly, but also in relation to one another. To clean and sterilize the valve arrangement in the region of the leakage space, for example, the upper valve disk is slightly-lifted upward, so that it comes out of engagement with its valve seat. The lower valve disk in this case remains in its closing position. A cleaning medium can then be conducted under high pressure, which may be, for example, around 3 bar, into the leakage space via the upper pipeline. The cleaning medium then has to be discharged through the lower valve disk, which continues to bear sealingly against its valve seat, for which purpose the lower valve disk has a drainage portion which has at least one drainage orifice. In the known valve device, a plurality of small orifices are provided, the overall cross section of which amounts to less than half the opening cross section of each of the connection pieces. The tubular extension of the lower valve disk through which the cleaning medium flows out also has an opening cross section which is likewise at most half as large as the opening cross section of each of the connection pieces. Moreover, the overall cross section of the orifices in the lower valve disk is also markedly smaller than the opening cross section of the connecting orifice.
If, then, as described above, the leakage space between the two valve disks is acted upon by a cleaning medium of high pressure, for example through the upper connection piece, the cleaning medium cannot flow out through the drainage orifices in the drainage portion to the same extent as it is supplied through the connection piece. The result is that an additional overpressure builds up in the leakage space and may lead to the lower valve disk being moved from its valve seat, so that the cleaning medium passes into the second pipeline, which must in any case, however, be avoided.
In order to avoid this, either the leakage space would have to be acted upon, to be cleaned, with a lower throughflow rate and a lower pressure, although this may be detrimental to the cleaning action, or the lower valve disk or the upper valve disk, depending on whether the cleaning medium is supplied through the lower or the upper pipeline, would have to be held reliably in the closing position by means of a corresponding additional holding force.
Recent standards demand that the maximum cross section of each connection piece of the pipeline must correspond approximately to the cross-sectional opening of the leakage orifice of the lower valve disk. This could be implemented by reducing the opening cross section of the connection pieces, although this reduces the productivity of a device in which such a valve device is installed. The abovementioned requirement is not fulfilled by the known valve device.
However, solving this problem by increasing the overall opening cross section of the drainage orifices in the lower valve disk is difficult because the lower valve disk has a middle connecting portion, via which the lower valve disk is connected to a valve stem serving for the movement drive of the lower valve disk. Increasing the overall opening cross section of the drainage portion of the lower valve disk would therefore necessarily lead to an increase in diameter of the lower valve disk, although this is undesirable.